When sensing pressure in aerospace or other commercial systems, it is often necessary to isolate the process fluid (e.g., fuel) from the electronic sensing elements associated with the pressure sensor. For example, referring to FIG. 1, a conventional pressure-sensor module 10 includes a header housing 20 including a high-pressure port 30 and a low-pressure oil-fill port 40. The high-pressure port 30 is configured to be in fluid communication with a first fluid-flow circuit, such as that associated with the aforementioned process fluid, having a variable or static pressure P1. The oil-fill port 40 is configured to be in fluid communication with a second fluid-flow circuit, which may be the ambient, having a variable or static pressure P2. The module 10 further includes an oil-fill volume 50 defined by a compressive coupling member 60 and sealing off a pressure-sensor assembly 70 from the process fluid. The oil-fill volume 50 is filled through the oil-fill port 40 with inert oil (not shown) and then sealed with a plug 80 inserted into the oil-fill port 40. In normal configurations, the oil-fill port 40 is loaded with the plug 80 subject to the pressure differential between P1 and P2. Loading of the plug 80 under such conditions can result in failure of the plug seal, resulting in sensor failure. To overcome this high loading, the ports are made with thick walls and the plug 80 loaded with deep-penetration sealing welds.